Automatic temperature responsive battery charging circuit

ABSTRACT

A charger for charging a battery at a first predetermined rate and automatically terminating said charge rate when the battery temperature rises, in response to the charging current, to a point indicating full charge. The battery has a thermistor mounted therein which changes resistance as the battery temperature changes. The charger includes a charging circuit and silicon controlled rectifier in series with the battery. A sensing circuit, coupled to the thermistor, senses a thermistor resistance indicative of less than a full charge and changes from a first to a second state. If the thermistor resistance indicates a full charge, the sensing circuit changes from the second to the first state. A switch circuit connected to the sensing circuit and the rectifier gate electrode is responsive to changes from the first to the second state to trigger the rectifier into conduction and allow charging of the battery at the predetermined rate. A latch circuit connected to the sensing circuit and rectifier gate electrode operates in response to the sensing circuit changing from the second to the first state to inhibit further conduction of the silicon controlled rectifier. The latch circuit is deenergized, allowing further conduction of the silicon controlled rectifier, by removal of the battery from the battery charger.

United States Patent Bogut et al.

[451 May 30, 1972 [54] AUTOMATIC TEMPERATURE RESPONSIVE BATTERY CHARGINGCIRCUIT [72] inventors: Henry A. Bogut; Leon Jasinski, both of Chicago,Ill.

[52] US. Cl ..320/36, 320/39 [58] Field of Search ..320/35, 36, 22, 39

[56] References Cited UNITED STATES PATENTS 3,457,489 7/1969 Gentry, Jr.et al. ..320/35 X 3,534,241 10/1970 Wilson et al. .320/35 X 3,531,7069/1970 Mullersman ..320/35 X Primary Examiner-J. D. Miller AssistantExaminerRobert J. Hickey Att0rneyVincent J. Rauner and L. N. Arnold [57]ABSTRACT A charger for charging a battery at a first predetermined rateand automatically terminating said charge rate when the bat- .terytemperature rises, in response to the charging current, to a pointindicating full charge. The battery has a thermistor mounted thereinwhich changes resistance as the battery temperature changes.

The charger includes a charging circuit and silicon controlled rectifierin series with the battery. A sensing circuit, coupled to thethermistor, senses a thermistor resistance indicative of less than afull charge and changes from a first to a second state. If thethermistor resistance indicates a full charge, the sensing circuitchanges from the second to the first state.

A switch circuit connected to the sensing circuit and the rectifier gateelectrode is responsive to changes from the first to the second state totrigger the rectifier into conduction and allow charging of the batteryat the predetermined rate. A latch circuit connected to the sensingcircuit and rectifier gate electrode operates in response to the sensingcircuit changing from the second to the first state to inhibit furtherconduction of the silicon controlled rectifier. The latch circuit isde-energized, allowing further conduction of the silicon controlledrectifier, by removal of the battery from the battery charger.

16 Claims, 1 Drawing Figure Patented May 30, 1972 M/ ATTY.

INVENTORS HENRY A. BOGUT LEON JASINSKI AUTOMATIC TEMPERATURE RESPONSIVEBATTERY CHARGING CIRCUIT BACKGROUND OF THE INVENTION One type of batterycharger commonly employed for charging batteries senses the terminalvoltage of the battery and provides a charging current to the batteryuntil the terminal voltage rises to a point indicating the battery isfully charged. When such chargers are used to rapidly charge a battery,that is, provide a high charging current to the battery in order torecharge it in a short period of time, it has been found that they arenot consistent in fully charging the batteries. This occurs becausevariations in battery resistance from unit to unit, and changes inbattery resistance due to aging, temperature or various chargingmethods, can cause a change in the terminal voltage to which the batterymust be charged. If the terminal voltage increases, the charger will notsupply enough current to charge the battery to the desired voltage. Ifthe terminal voltage decreases, the charger will overcharge the batteryif it is charged to the terminal voltage. Overcharging a sealed batterycan damage the battery thus reducing its useful life, and can also causeoverheating and gassing, creating the possibility of an explosion.

It has been found that a battery may be charged at a high chargingcurrent or rate to substantially 100 percent of its charge capacity bymeasuring the temperature rise in the battery as itis being charged.This temperature rise is directly related to the condition of charge ofthe battery, and will remain so related even though other physicalcharacteristics of the battery may change or deteriorate.

Although charging systems which measure battery temperature rise havebeen previously employed, all required some manual settings to thesystem in order to initiate or terminate charging. The systems arecommonly used with vented rather than sealed cells, and require manualattachment of the temperature sensing components and charging circuits.Those that automatically initiate charging are so designed as tocontinuously provide a dangerous high voltage or high current at theexposed charging terminals. Such systems are primarily designed forcharging batteries, such as automobile batteries, where large andexpensive mechanisms can be employed, and are operated by trainedpersonnel. In an application where it is necessary to charge a greatmany portable radio batteries, and the batteries are connected byuntrained personnel, a small inexpensive and highly automated unit isdesirable. It is also desirable that the system employ no mechanical orelectromechanical switching components, thus minimizing adjustment andmaintenance.

SUMMARY OF THE INVENTION An object of this invention is to provide anautomatic battery charger capable of charging all batteries of the sametype to substantially l percent of full charge capacity.

Another object of this invention is to provide an automatic batterycharger which employs no relays or mechanical switches.

Yet another object of this invention is to provide an automatic batterycharger which senses the temperature rise in the battery due to chargingcurrent, terminates charging when a temperature indicating full chargehas been reached, and inhibits further charging.

Still another object of this invention is to provide an automaticcharger which is reset, allowing it to again charge, by removing ordisconnecting the battery from the charger.

A further object of this invention is to provide an automatic batterycharger wherein the exposed charging terminals do not carry a dangeroushigh current until the battery has been connected thereto.

In practicing this invention a charger is provided for automaticallyrapidly charging a battery at a-predetermined chargingrate, andautomatically terminating said charging rate when the batterytemperature rises, in response to charging current, to a pointindicating full charge. The battery includes a themristor which changesresistance as the temperature of the battery varies.

The charger includes a charging circuit and silicon controlled rectifierin series with the battery. When the battery is connected to thecharger, a bias circuit is coupled to the thermistor which develops avoltage in response to the current through the thermistor that varies inaccordance with the temperature, and therefore state of charge, of thebattery. A trigger circuit is coupled to the bias circuit and isresponsive to the voltage developed thereby, indicative of less thanfull charge, to change from a first to a second state. The triggercircuit is also responsive to a bias voltage indicating full charge tochange from the second to the first state.

A first switching circuit connected to the trigger circuit is responsiveto the change from the first to the second state to render the siliconcontrolled rectifier in series with the battery conductive, allowing thebattery to charge at the predetermined rate. A turn-ofi circuitconnected to the trigger circuit and the silicon controlled rectifier isresponsive to the change from the second to the first state to renderthe silicon controlled rectifier in series with the batterynon-conductive, and inhibit further conduction. The tum-off circuit isreset allowing further conduction of the silicon controlled rectifierwhen the battery is removed from the charging device.

Contacts on the battery housing and contacts in the charger mate whenthe battery is inserted into the charger automatically providing allnecessary interconnections. This allows the charger to be used byuntrained personnel. As the bias circuit will not be operative until thebattery is inserted into the charger, the silicon controlled rectifierwill by non-conductive. When the silicon controlled rectifier isnon-conductive, a high current charging path is not provided forcharging the battery. The exposed charging terminals of the batterycharger do not therefore carry a dangerous high current or voltage whenthe battery is not in the charger. When the battery is inserted, itcovers the tenninals preventing accidental contact by untrainedpersonnel.

THE DRAWING The single FIGURE is a schematic diagram of an automaticrapid charger circuit incorporating the features of this invention, andthe battery which is charged by the charger and which has a thermistormounted therein.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawingthere is shown a schematic diagram of an automatic battery chargercircuit incorporating the features of this invention. A battery unit 10which is to be charged is shown along with the charger circuitry.Battery unit 10 includes a battery 1 1, and a thermistor 12.

Battery 11 is of the rechargeable type and may or may not be sealed. Thetemperature of a rechargeable battery such as battery 1 1 rises, inresponse to an applied charging current, as the battery approaches fullcharge. This rising temperature characteristic remains consistent evenwhen the battery is charged at an extremely high charging rate. Itremains substantially the same for all batteries of a given type andconfiguration, notwithstanding variations in battery resistance, orterminal voltage, or variations due to aging and various charging rates.For this reason, measurement of the temperature rise in a battery is themost precise method of monitoring state of charge of a battery.

Therrnistor 12 is physically mounted within the housing of unit 10 andis responsive to a change in battery temperature to change resistance.Therrnistor 12 is a positive temperature coefiicient thermistor selectedsuch that its resistance will substantially increase at a temperaturecorresponding to a battery temperature indicative of full charge on thebattery.

Battery unit 10 includes contacts 13, 14 and 15. Contacts 13 and 14 areeach connected to one terminal of battery 11. Terminal 15 is connectedto one end of thermistor 12. The other end of thermistor 12 is connectedto terminal 14 and its associated battery terminal. As can be seen,battery 11 and thermistor 12 are connected in series between terminals13 i and 15. Contacts 13, 14 and 15 are physically secured to onesurface of battery unit 10 such that when the battery is inserted intothe charger the contacts will mate with the corresponding contactsmounted on the charger. The weight of the battery unit 10 when the unitis inserted into the charger will insure an adequate connection betweenthe charger contacts and battery contacts. Battery unit 10 will coverthe charger contacts when inserted, preventing accidental contact byuntrained personnel who may use the device.

The automatic battery charger circuit includes a transformer 18 having aprimary winding 19 supplied from a commercial alternating current sourceby plug 20. Secondary winding 21 of transformer 18 is connected tobridge rectifier 22, having diodes 22a, b, c and d connected in therespective legs of the bridge network in conventional fashion. Thejunction of diodes 22b and 220 is connected to terminal 23. Terminal 23provides one contact terminal for connection of the charger to batteryunit 10. Terminal 24 of the charger couples terminal 14 of battery unit10 to the charger circuit. A silicon controlled rectifier (SCR) 25, hasone principal electrode 81 coupled to terminal'24, and a secondprincipal electrode 82 coupled to resistor 26. Resistor 26 is coupled tothe junction of diodes 22a and 22d in bridge rectifier 22 to complete aseries fast charging path for battery 11 in battery unit 10. Coupled inparallel with SCR 25 and resistor 26 is resistor 27, a

high resistance which provides a slow charge, or trickle charge path forbattery 1 1 when unit 10 is installed in the charger.

Operation of the charger circuit is as follows; Battery unit 10 isinserted into the charger housing making contact with contacts 23, 24and 28. Thermistor 12 in battery unit 10, being a positive temperaturecoefficient thermistor, initially has relatively low resistance,allowing current to flow therethrough to emitter 30 of transistor 31.Transistor 31 is biased into conduction by the bias voltage supplied bybridge rectifier 22 and battery 11 through contacts 14 and 24, and

diodes 32, to base 33 of transistor 31. Transistor 31 acts to amplifythe current flowing through thermistor 12. The amplified currentappearsat collector 34 causing a voltage to be developed across resistor 35.The voltage developed across resistor 35 is coupled through resistor 36to diode 37 and capacitor 38 where it is filtered to produce a DCvoltage that varies in accordance with the current through thermistor12. This voltage is coupled to base 40 of transistor 42 in Schmitttrigger 41. As the current passing through thermistor 12 varies inaccordance with the temperature of the battery, the voltage developed atbase 40 of Schmitt trigger 41 also must vary in accordance with thetemperature of the battery.

Schmitt trigger 41 consists of transistors 42 and 43, with transistor 42being normally non-conductive and transistor 43 conductive. The voltagedeveloped at base 40 of transistor 42, when thermistor 12 has arelatively low resistance, is sufficient to cause Schmitt trigger 41 tochange states. That is, transistor 42 will saturate. When transistor 42saturates, it causes transistor 43, the other half of Schmitt trigger41, to become non-conductive, causing the voltage at collector 44 oftransistor 43 to increase or go to a more positive logic level. Schmitttrigger 41 has now changed from a first to a second state. The increasedvoltage at collector 44 is coupled through resistor 46 to base 47 oftransistor switch 48. Transistor 48 has collector 49 connected to asource of DC potential at diode 50. Emitter 51 of transistor 48 iscoupled to gate 29 of SCR 25 through resistor 100. The increased voltagecoupled to base 47 of transistor 48 forward biases transistor 48,coupling the DC voltage from collector 49 through emitter 51 andresistor 100 to gate 29 of SCR 25. The DC voltage coupled to gate 29causes SCR 25 to conduct and provide a high current charging path forbattery 11. The current through this high current charging path islimited by resistor 26.

As battery 11 approaches full charge, its temperature rises due to thehigh charging current. As previously stated, this temperature risecauses the resistance of thermistor 12 to substantially increase. Withthe resistance of thermistor 12 substantially increased, the currentcoupled to amplifier transistor 31, and the voltage developed acrossresistor 35 will decrease. The rectified voltage then coupled to base 40of transistor 42 will also decrease to a point which causes transistor42 to become non-conductive. When transistor 42 of Schmitt trigger 41becomes non-conductive, transistor 43 will again begin to conduct,causing the voltage at collector 44 of transistor 43 to suddenlydecrease. Schmitt trigger 41 has now changed from the second back to thefirst state. The negative going change in voltage at collector 44 oftransistor 43 is coupled through capacitor 55 and resistor 56 to base 57of transistor 58. Transistor 58 is rendered temporarily non-conductiveby the negative going voltage or pulse, causing collector 59 totemporarily increase in voltage and become more positive. Thistemporarily increased positive voltage or pulse is coupled throughresistor 60 to gate 63 of SCR 64, causing SCR 64 to conduct. Diode 50coupled to terminal 24, and capacitor 68 coupled to the cathode of diode50 act to rectify the voltage coupled from rectifier bridge 22 andbattery 11, and produce a pure DC signal at anode of SCR 64. With a pureDC signal at anode 65, SCR 64 will continue conducting until the DCvoltage at anode 65 is removed. When SCR 64 conducts, a voltage isdeveloped across resistor 69 coupled between cathode 66 of SCR 64 andground potential. This voltage is coupled through resistor 70 to base 73of transistor 74, causing transistor 74 to conduct. With transistor 74conducting, collector 75 of transistor 74 approaches the groundpotential at emitter 76. Collector 75 is coupled to gate 29 of SCR 25.With a ground potential at gate 29, caused by the ground potential atcollector 75 of transistor 74, SCR 25 will be rendered non-conductivewhen the potential at anode 81 of SCR 25 drops to 0 volts. This occurswhen the rectified DC pulses, coupled through battery-ll from rectifiernetwork 22 drop to 0 volts. With SCR 25 cut-off, the rapid charging pathis broken, allowing battery 11 to be maintained in a charged conditionthrough the charging path provided by slow, or trickle charge resistor27.

When the rapid charging has terminated, battery unit 10 will begin tocool to room temperature due to the elimination of the high chargingcurrent. As the battery temperature decreases, the resistance ofthermistor 12 will decrease, again allowing more current to be coupledthrough amplifier 31 to resistor 35. The rectified voltage coupled tobase 40 of Schmitt trigger 41 will increase causing the Schmitt triggerto again change states, or change from a first to a second state. Thechange of state causes collector 44 of transistor 43 to again increase.The increased voltage is coupled to transistor 48 causing it to conductand couple the DC voltage from collector 49 to emitter 51. Althoughemitter 51 is coupled to gate electrode 29 of SCR 25, it will not causeconduction of SCR 25. This is because transistor 74 remains conductive,acting as a switch to shunt any voltage appearing at gate 29 of SCR 25to ground, and preventing energization of SCR 25. Transistor 74 willremain conductive as long as SCR 64 remains conductive. SCR 64 willremain conductive as long as battery unit 11 is connected to thecharger. When battery unit 1 1 is removed from the charger, the DCpotential coupled from terminal 14 through rectifier 50 to anode 65 ofSCR 64 is removed, causing SCR 64 to stop conducting. With SCR 64rendered nonconductive, transistor 74 no longer provides a ground pathfor gate 29 of SCR 25, allowing SCR 25 to conduct when a positivevoltage is coupled to gate 29.

The network consisting of resistors 85 and 86 and capacitor 87 acts as adelay network, preventing the voltage at gate 63 of SCR 64 from buildingup before the voltage at anode 65. With this delay network, insertion ofa battery or connection of the AC plug 20 to a source of AC potential,will not cause SCR 64 to fire and inhibit operation of the fast chargingcircuit.

As previously stated, transistor 31 is biased into conduction by biasvoltage supplied by bridge rectifier 22 and battery 1 1. It will not berendered conductive unless the proper combined voltage is supplied toterminals, 24 and 28, and the proper resistance is coupled thereacross.A human hand, or a metallic object shorting terminals 23, 24 and 25together, will not forward bias transistor 31. Conduction of amplifier31 is necessary before SCR 25, which completes the high current chargingpath, can be rendered conductive. The high current charging path cannottherefore be rendered operative when battery unit is removed and thecharging terminals are exposed. The voltage developed at terminal 23 bybridge circuit 22, is low and will not be harmful if a person shouldaccidentally short same to terminal 24 or 28. Although a current path isstill provided by resistor 27, the resistance value. is high, preventinga dangerous amount of current from flowing therethrough.

The automatic rapid charger circuit also includes indicating means toindicate when the unit is being charged, or that rapid charge has beencompleted. The first indicating circuit consists of indicator light 90and SCR 91, series connected from the junction of rectifiers 22c and 22dto the junction of rectifiers 22a and 22d. Gate 92 of SCR 91 isconnected through resistors 93 and 94 to terminal 24 of the automaticcharger unit. When battery unit 10 is installed in or connected to thecharger, SCR 91 will be rendered conductive, causing light 90 toilluminate indicating the unit 10 is charging.

A second indicating circuit is included to show charge completion. Thecircuit includes lamp 95 and SCR 96 connected in parallel with lamp 90and SCR 9]. Gate 97 of SCR 96 is coupled through resistor 98 to cathode66 of SCR 64. When SCR 64 conducts, the voltage developed acrossresistor 69 is also coupled to gate electrode 97 of SCR 96, causing itto conduct allowing illumination of lamp 95. Lamp 95 indicates thatcharging is completed. The conduction of SCR 96 also forward biasesdiode 99 coupled from the junction of lamp 95 and SCR 96 to the junctionof resistors 93 and 94. With diode 99 forward biased, the voltagedeveloped at gate 92 or SCR 91 decreases, causing SCR 91 to becomenon-conductive between the next rectified DC line pulse.

As can be seen, an automatic battery charger circuit has been providedfor rapidly charging a rechargeable battery to substantially 100 percentof its full charge capacity. The automatic battery charger employs nomechanical switches or relays in order to initiate or terminatecharging. The charger senses the temperature rise in the battery due tocharging current, terminates charging when a temperature indicating fullcharge has been reached, and inhibits further charging. The charger isso designed that the exposed charging terminals do not carry a dangeroushigh current until the battery has been connected thereto. The simpleand fully automated circuit operation of the charger allows it to beconveniently used by untrained personnel.

What is claimed is:

l. A device for charging a battery from a source of altemating currentwherein the battery includes a temperature variable resistor in serieswith the battery which changes resistance and current therethrough asthe battery temperature changes in response to charging current, saiddevice including in combination, a charging circuit including rectifiermeans coupled to the source of alternating current and to the batteryfor applying a unidirectional charging current to said battery, a firstsilicon controlled rectifier including a pair of principal electrodes inseries with the battery and said charging circuit for passing saidunidirectional charging current to allow charging of said battery, saidfirst silicon controlled rectifier having a gate electrode forcontrolling conduction thereof, first circuit means coupled to saidtemperature variable resistor and responsive to the current therethroughto develop a first voltage varying in level in accordance with thetemperature of said battery, semiconductor trigger circuit means coupledto said first circuit means and responsive to said first voltageexceeding a first predetermined level to change from a first to a secondstate and responsive to said first voltage decreasing below saidpredetermined level to change from the second to first state, firstswitch means coupled to said semiconductor trigger circuit means andsaid gate electrode for triggering said first rectifier into conductionby said change of state whereby said battery is allowed to charge, andturn-off circuit means coupled to said semiconductor trigger circuitmeans and said gate electrode and responsive to said trigger circuitmeans changing from said second to said first state to trigger saidfirst rectifier into non-conduction whereby said battery is no longercharged.

2. The device of claim 1 wherein said first switch means includes, afirst transistor coupled to said rectifier gate electrode and to saidsemiconductor trigger circuit means and responsive to the change fromthe first to the second state to trigger said first rectifier intoconduction.

3. The device of claim 2 wherein said turn-off circuit means includes, asecond silicon controlled rectifier having a gate electrode coupled tosaid semiconductor trigger circuit means and a principal electrodecoupled to the battery, said second rectifier being rendered conductivein response to said semiconductor trigger circuit changing from thesecond to the first state, said first rectifier being renderednon-conductive and further conduction thereof inhibited, in response tosaid second rectifier conduction, said second rectifier being renderednon-conductive by removal of said battery from said device whereby saidfirst rectifier may be rendered conductive in response to said firstswitch means,

4. The device of claim 3 wherein said turn-off circuit further includes,a second transistor coupled to said first rectifier gate electrode andto a principal electrode of said second rectifier, said secondtransistor operative in response to conduction of said second rectifierto render said first rectifier non-conductive and inhibit furtherconduction of same.

5. The device of claim 4 wherein said tum-off circuit means furtherincludes, a third transistor coupled to said second rectifier gateelectrode and to said semiconductor trigger circuit means, said thirdtransistor operative in response to said trigger circuit means changingfrom the second to the first state to trigger said second rectifier intoconduction.

6. The device of claim 5 wherein said'semiconductor trigger circuitmeans is a Schmitt trigger.

7. The device of claim 6 further including, indicator circuit meanscoupled to said charging circuit and to said battery and responsive tothe charging current flowing therethrough to indicate charging of saidbattery. I

8. The device of claim 7 further including second indicator circuitmeans coupled to said charging circuit and to said second rectifier andresponsive to conduction of said second rectifier to indicate completionof charging.

9. The device of claim 8 wherein said first and second indicator circuitmeans includes, a lamp coupled to said charging circuit for providingsaid indication, and a silicon controlled rectifier having first andsecond principal electrodes in series with said lamp and chargingcircuit, said silicon controlled rectifiers each including a gateelectrode for controlling conduction thereof, said rectifier gateelectrode in said first indicating means being coupled to said batteryand responsive to charging current flowing therethrough to render saidrectifier conductive, said rectifier gate electrode in said secondindicating means being coupled to said second rectifier and responsiveto conduction thereof to render said rectifier conductive.

10. A device for automatically charging a battery having a voltagethereacross from a source of alternating current at a predeterminedcharge rate and automatically terminating said charge rate when thebattery temperature rises to a first level indicating full charge, inresponse to the charging current, and wherein the device is reset byremoval of the battery from the device, said device including incombination, a charging circuit including rectifier means series coupledwith said battery and coupled to said source of alternating current forapplying a unidirectional charging current to said battery, a firstsilicon controlled rectifier having a pair of principal electrodes inseries with said battery and said charging circuit for passing saidundirectional charging current to allow charging of said battery, saidfirst rectifier having a first gate electrode for controlling conductionthereof, first circuit means coupled to said battery and responsive to abattery temperature below said first level to switch from a first to asecond state, said first circuit means responsive to a batterytemperature above said first level to switch from the second to thefirst state, first switch means connected to said first circuit meansand the first rectifier gate electrode and responsive to a change fromthe first to the second state to develop a trigger signal, said firstrectifier operative only in response to said trigger signal to conductwhereby said battery is allowed to charge, latch circuit means coupledto said first circuit means and said first rectifier gate electrode andincluding a second silicon controlled rectifier having a first principalelectrode coupled to the battery and a gate electrode coupled to saidfirst circuit means, said second rectifier being rendered conductive inresponse to said first circuit changing from the second to the firststate, and further being held conductive by said battery voltage coupledthereto, said first rectifier being rendered non-conductive and furtherconduction of same inhibitedin response to said second rectifierconduction, said second rectifier being rendered non-conductive bytermination of said battery voltage coupled thereto, termination of saidbattery voltage being effected only by removal of said battery from saiddevice.

11. The device of claim 10 wherein said battery further includes, atemperature variable resistor mounted therein in series with the batterywhich changes resistance and current therethrough as the batterytemperature varies, and said first circuit means includes, bias circuitmeans coupled to said temperature variable resistor and responsive tothe current therethrough to develop a bias voltage varying in accordancewith the temperature of said battery, said first circuit means furtherincluding semiconductor trigger circuit means coupled to said biascircuit means and responsive to said bias voltage exceeding a firstpredetennined level to change from the first to the second state, saidtrigger circuit means being further responsive to said first voltagedecreasing below said first predetermined level to change from thesecond to the first state.

12. The device of claim 11 wherein said first switch means includes, afirst transistor coupled to said semiconductor trigger circuit means,and to said first rectifier gate electrode, said first transistor beingresponsive to said trigger circuit means changing from the first to thesecond state to trigger said first rectifier into conduction,

13. The device of claim 12 wherein said latch circuit means furtherincludes, second switch means coupled to said first rectifier gateelectrode and to a second principal electrode of said second rectifier,and operative in response to conduction of said second rectifier torender said first rectifier non-conductive and inhibit furtherconduction of same.

14. The device of claim 13 wherein said latch circuit means furtherincludes, a third switch means coupled to said second rectifier gateelectrode and said trigger circuit means, said third switch meansoperative in response to said trigger circuit changing from the secondto the first state to trigger said second rectifier into conduction.

15. The device of claim 11 wherein said semiconductor trigger circuitmeans is a Schmitt trigger.

16. The device of claim 15 wherein said second and third switch meansare transistors.

1. A device for charging a battery from a source of alternating currentwherein the battery includes a temperature variable resistor in serieswith the battery which changes resistance and current therethrough asthe battery temperature changes in response to charging current, saiddevice including in combination, a charging circuit including rectifiermeans coupled to the source of alternating current and to the batteryfor applying a unidirectional charging current to said battery, a firstsilicon controlled rectifier including a pair of principal electrodes inseries with the battery and said charging circuit for passing saidunidirectional charging current to allow charging of said battery, saidfirst silicon controlled rectifier having a gate electrode forcontrolling conduction thereof, first circuit means coupled to saidtemperature variable resistor and responsive to the current therethroughto develop a first voltage varying in level in accordance with thetemperature of said battery, semiconductor trigger circuit means coupledto said first circuit means and responsive to said first voltageexceeding a first predetermined level to change from a first to a secondstate and responsive to said first voltage decreasing below saidpredetermined level to change from the second to first state, firstswitch means coupled to said semiconductor trigger circuit means andsaid gate electrode for triggering said first rectifier into conductionby said change of state whereby said battery is allowed to charge, andturn-off circuit means coupled to said semiconductor trigger circuitmeans and said gate electrode and responsive to said trigger circuitmeans changing from said second to said first state to trigger saidfirst rectifier into non-conduction whereby said battery is no longercharged.
 2. The device of claim 1 wherein said first switch meansincludes, a first transistor coupled to said rectifier gate electrodeand to said semiconductor trigger circuit means and responsive to thechange from the first to the second state to trigger said firstrectifier into conduction.
 3. The device of claim 2 wherein saidturn-off circuit means includes, a second silicon controlled rectifierhaving a gate electrode coupled to said semiconductor trigger circuitmeans and a principal electrode coupled to the battery, said secondrectifier being rendered conductive in response to said semiconductortrigger circuit changing from the second to the first state, said firstrectifier being rendered non-conductive and further conduction thereofinhibited, in response to said second rectifier conduction, said secondrectifier being rendered non-conductive by removal of said battery fromsaid device whereby said first rectifier may be rendered conductive inresponse to said first switch means.
 4. The device of claim 3 whereinsaid turn-off circuit further includes, a second transistor coupled tosaid first rectifier gate electrode and to a principal electrode of saidsecond rectifier, said second transistor operative in response toconduction of said second rectifier to render said first rectifiernon-conductive and inhibit further conduction of same.
 5. The device ofclaim 4 wherein said turn-off circuit means further includes, a thirdtransistor coupled to said second rectifier gate electrode and to saidsemiconductor trigger circuit means, said third transistor operative inresponse to said trigger circuit means changing from the second to thefirst state to trigger said second rectifier into conduction.
 6. Thedevice of claim 5 wherein said semiconductor trigger circuit means is aSchmitt trigger.
 7. The device of claim 6 further including, indicatorcircuit means coupled to said charging circuit and to said battery andresponsive to the charging current flowing therethrough to indicatecharging of said battery.
 8. The device of claim 7 further includingsecond indicator circuit means coupled to said charging circuit and tosaid second rectifier and responsive to conduction of said secondrectifier to indicate completion of charging.
 9. The device of claim 8wherein said first and second indicator circuit means includes, a lampcoupled to said charging circuit for providing said indication, and asilicon controlled rectifier having first and second principalelectrodes in series with said lamp and charging circuit, said siliconcontrolled rectifiers each including a gate electrode for controllingconduction thereof, said rectifier gate electrode in said firstindicating means being coupled to said battery and responsive tocharging current flowing therethrough to render said rectifierconductive, said rectifier gate electrode in said second indicatingmeans being coupled to said second rectifier and responsive toconduction thereof to render said rectifier conductive.
 10. A device forautomatically charging a battery having a voltage thereacross from asource of alternating current at a predetermined charge rate andautomatically terminating said charge rate when the battery temperaturerises to a first level indicating full charge, in response to thecharging current, and wherein the device is reset by removal of thebattery from the device, said device including in combination, acharging circuit including rectifier means series coupled with saidbattery and coupled to said source of alternating current for applying aunidirectional charging current to said battery, a first siliconcontrolled rectifier having a pair of principal electrodes in serieswith said battery and said charging circuit for passing saidundirectional charging current to allow charging of said battery, saidfirst rectifier having a first gate electrode for controlling conductionthereof, first circuit means coupled to said battery and responsive to abattery temperature below said first level to switch from a first to asecond state, said first circuit means responsive to a batterytemperature above said first level to switch from the second to thefirst state, first switch means connected to said first circuit meansand the first rectifier gate electrode and responsive to a change fromthe first to the second state tO develop a trigger signal, said firstrectifier operative only in response to said trigger signal to conductwhereby said battery is allowed to charge, latch circuit means coupledto said first circuit means and said first rectifier gate electrode andincluding a second silicon controlled rectifier having a first principalelectrode coupled to the battery and a gate electrode coupled to saidfirst circuit means, said second rectifier being rendered conductive inresponse to said first circuit changing from the second to the firststate, and further being held conductive by said battery voltage coupledthereto, said first rectifier being rendered non-conductive and furtherconduction of same inhibited in response to said second rectifierconduction, said second rectifier being rendered non-conductive bytermination of said battery voltage coupled thereto, termination of saidbattery voltage being effected only by removal of said battery from saiddevice.
 11. The device of claim 10 wherein said battery furtherincludes, a temperature variable resistor mounted therein in series withthe battery which changes resistance and current therethrough as thebattery temperature varies, and said first circuit means includes, biascircuit means coupled to said temperature variable resistor andresponsive to the current therethrough to develop a bias voltage varyingin accordance with the temperature of said battery, said first circuitmeans further including semiconductor trigger circuit means coupled tosaid bias circuit means and responsive to said bias voltage exceeding afirst predetermined level to change from the first to the second state,said trigger circuit means being further responsive to said firstvoltage decreasing below said first predetermined level to change fromthe second to the first state.
 12. The device of claim 11 wherein saidfirst switch means includes, a first transistor coupled to saidsemiconductor trigger circuit means, and to said first rectifier gateelectrode, said first transistor being responsive to said triggercircuit means changing from the first to the second state to triggersaid first rectifier into conduction.
 13. The device of claim 12 whereinsaid latch circuit means further includes, second switch means coupledto said first rectifier gate electrode and to a second principalelectrode of said second rectifier, and operative in response toconduction of said second rectifier to render said first rectifiernon-conductive and inhibit further conduction of same.
 14. The device ofclaim 13 wherein said latch circuit means further includes, a thirdswitch means coupled to said second rectifier gate electrode and saidtrigger circuit means, said third switch means operative in response tosaid trigger circuit changing from the second to the first state totrigger said second rectifier into conduction.
 15. The device of claim11 wherein said semiconductor trigger circuit means is a Schmitttrigger.
 16. The device of claim 15 wherein said second and third switchmeans are transistors.